Seven air crew from a Cornwall air base have been killed in a collision between two Sea King helicopters in the Gulf.
The six British and one American crew members from RNAS Culdrose, near Helston, died after an accident at about 0115 GMT (0415 local time) on Saturday over international waters.
It is thought that one of the helicopters had been refuelling on board the aircraft carrier HMS Ark Royal, while the other was believed to have been returning from a mission.
The helicopters were part of the Royal Navy's 849 Squadron Airborne Early Warning team at the Helston base.
A British military spokesman said: "There are believed to be no survivors. The incident was not the result of enemy action.
Sea King AEW
Brought into service after the Falklands conflict
Can detect low flying aircraft trying to attack surface ships
Maximum speed of 125 knots
Operated by a crew of three - one pilot and two observers
They are used to protect aircraft carriers
"Further details will be released as soon as possible after next of kin have been informed."
The Ark Royal's Captain Alan Massey said the deaths were caused by a "tragic accident" near the Royal Navy's flagship.
He said: "One of the aircraft was just leaving the deck, while the other was in its final stages of recovery to the ship some five miles out when they collided."
He paid tribute to the crews, saying: "These are very professional and superb aviators. They have been doing very important missions.
"They've been operating in arduous conditions, day in and day out for weeks on end now, providing essential surveillance support to Royal Marines occupying the al-Faw peninsula support."
Group Captain Al Lockwood, chief spokesman for the British forces, said an investigation will follow.
He said: "We'll be examining every aspect of their flight operations.
"Very much at the moment our thoughts are with any of the crew members' families and friends, who are obviously being notified of this tragic accident."
Appearing to rule out mechanical failure, he added: "All coalition aircraft are maintained to the highest of standards".
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Despite the deaths, Captain Massey said the ship's work would continue and members of the same squadron had already been sent out.
He said: "I know that what they would have said to us now that there is a mission to do...we have marines on the ground who need our support."
It is the second loss of South West-based troops since war in Iraq started.
On Friday, eight servicemen from Plymouth-based 3 Commando died in a helicopter crash in northern Kuwait.
The troops died when a US CH-46 Sea Knight helicopter crashed several miles south of the Iraqi border. Four US service personnel also died in the incident.